1. Field of the Invention
The present invention relates to solventless organosilicon compositions comprising at least one organopolysiloxane compound containing a hyroxysilyl group and a crosslinking agent containing alkoxysilyl groups. The subject compositions are especially useful for imparting water-repellant properties to a variety of substrates, such as asbestos or cellulose derivatives or various synthetic materials. Such compositions are also useful for imparting good non- or anti-stick properties to various substrates. The compositions according to the invention thus pave the way for the manufacture of non-stick paper coatings and also gaskets for a variety of industries, such as the automotive industry.
2. Description of the Prior Art
Solventless organosilicon compositions have to date been proposed to this art for the treatment of various substrates, such as paper and plastic sheet materials; these compositions typically comprise low-viscosity diorganopolysiloxanes comprising hydroxyl radicals at the ends of the polymer chain, and vinyl radicals, organohydrogenopolysiloxanes optionally comprising vinyl groups, and catalysts based on platinum or platinum derivatives (compare published French Application No. 2,283,934 and its first Addition thereto No. 2,318,204, and published French Applications Nos. 2,183,125, 2,209,607, 2,294,765 and 2,307,025). Same harden rapidly on the surface of the materials onto which they have been deposited in thin layers, and form coatings frequently having satisfactory non-stick properties.
These compositions have the advantage over those employed in solution, which are usually diluted to at least 5 times their weight with solvent (published French Application No. 2,273,835), of avoiding the setting-up of solvent-recovery equipment, which is sometimes dangerous and always expensive and bulky. However, the coatings obtained are limited as regards their utilization, and their use for the protection of foodstuffs has not hitherto been universally permitted by various national laws. Furthermore, inhibition phenomena have been observed, in particular in respect of metal derivatives contained in the materials to be treated. This last feature is of great importance in the manufacture of gaskets for the automotive industry.
The use of organic tin salts as catalysts for solventless compositions containing diorganopolysiloxanes blocked by hydroxyl radicals at the ends of the polymer chains, and organohydrogenopolysiloxanes (published French Application No. 2,291,254), does not bring about the desired improvements. In fact, these salts firstly have considerable toxicity and, secondly, tend to cause the compositions which they catalyze to gel very rapidly, at ambient temperature, when such compositions are placed in the coating tanks of industrial machines.
Various organosilicon compositions too have been proposed for impregnating the core of, or for making coatings on, composite materials comprising, for example, a metal base and coverings therefor of asbestos fibers. In general, these are organosilicon compositions which can be crosslinked when hot, under the action of peroxides, and which make it possible to obtain various gaskets which can be used, in particular, in the automotive industry. However, very thin coatings prove difficult to obtain by this technique. Furthermore, it is difficult to obtain thick gaskets having very good surface properties.